Method for making a phosphor screen of a cathode-ray tube

ABSTRACT

An improved method for making a phosphor screen of a cathode-ray tube in which light-exposed portions of a photosensitive layer of a shadow mask assembly are removed by washing the assembly with a detergent solution thereby providing definite light-transmissible holes in the photosensitive layer. Exposure of phosphor to light through the resulting shadow mask assembly provides a satisfactorily uniform pattern of phosphors.

ilititeel States Fatent n91 Takemoto et ai.

[ METHOD FOR MAKING A PHOSPHOR SCREEN OF A CATHODE-RAY TUBE [75]Inventors: Takeo Takeinoto; Yoshifumi Tomita, both of Mobara; llchiroljichi; Sajiro Maeda, both of Toyohashi, all of Japan [73] Assignee:Hitachi, Ltd., Tokyo, Japan [22] Filed: June 19, 1973 [21] Appl. No.:371,569

[30] Foreign Application Priority Data June 30, 1972 Japan 47-65000 52us. Cl 96/36.l, 96/44, 96/45 [51] Int. Cl G03c 5/00 [58] Field of Search96/36.], 36, 44, 45

[56] References Cited UNITED STATES PATENTS 2,961,314 11/1960 Amdurskyet a1. 96/361 Get. 15, 1974 3,070,441 12/1962 Schwartz 96/36.! 3,653,9014/1972 Etter 96/361 3,725,065 4/1973 Fadncr 96/361 3,775,116 11/1973Takemoto et a1 96/361 Primary ExaminerDavid Klein AssistantExaminer-Edward C. Kimlin Attorney, Agent, or Firm-Craig & Antonelli[57] ABSTRACT 5 Claims, 3 Drawing Figures 1 METHOD FOR MAKING APHOSPIIOR SCREEN OF A CATHODE-RAY TUBE The present invention relates toa method for making a phosphor screen of a cathode-ray tube or more inparticular to an improvement on the method for making a phosphor screenof a cathode-ray tube disclosed in French Pat. No. 7,143,315corresponding to U.S. Patent Ser. No. 204,020, now U.S. Pat. No.3,775,116, filed on Dec. 2, 1971.

In the method disclosed in the above-mentioned patent, light-exposedportions of a photosensitive layer are smaller in diameter than and inregistration with the shadow mask openings, and the photosensitive layerlies on a transparent layer which is in turn formed on the shadow mask,thus constituting a shadow mask assembly to be used for forming phosphordots smaller in diameter than the shadow mask openings on the innersurface of the cathode-ray tube. In the abovementioned method, thelight-exposed portions of the photosensitive layer remain unremoved overthe shadow mask. This results in the lack of concentricity and/orroundness of the phosphor dots formed, often causing a resultingphosphor dot screen on the inner surface of the panel to undergo theserious problem of uneveness.

Further, in removing the photosensitive layer and transparent layer fromthe shadow mask in order to recover a shadow mask after the formation ofthe phosphor screen, the shadow mask is liable to be damaged by thepresence of a bonding agent on the whole surface of the shadow mask.

An object of the present invention is to provide an improved methodofforming a phosphor screen of a cathode-ray tube without theabove-mentioned inconveniences.

The above and other objects, features and advantages will be madeapparent from the detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. I is a sectional viewv showing the essential parts of an unfinishedshadow mask assembly used'in the method of the invention;

FIG. 2 is a diagram showing a sectional view of the manner in which theshadow mask assembly is mounted on the frame; and

FIG. 3 is a sectional view showing the essential parts of the shadowmask assembly for explaining an embodiment of the present invention.

According to the present invention, there is provided a method formaking a phosphor screen of a cathoderay tube comprising the steps ofproviding a transparent layer on that surface of a shadow mask whichfaces the phosphor screen within the cathode-ray tube, the shadow maskbeing carried by a supporting frame, the transparent layer being capableof attenuating light passing therethrough, providing a photosensitivelayer on the transparent layer, exposing the photosensitive layer tolight through the shadow mask and transparent of the phosphor pattern,the shadow mask assembly is washed with a detergent solution to removethe light exposed portions of the photosensitive layer.

In FIGS. 1 to 3, same reference numerals designate similar members orelements.

First, a shadow mask 1 with openings of a predetermined diameter to befinally mounted on a cathode-ray tube is prepared, and a photosensitivesheet 2 consisting of a photosensitive layer 2a and a transparent layer2b constituting a base film for the photosensitive layer 2a is closelyattached, without being wrinkled, onto that surface la of the shadowmask 1 which is to face a phosphor screen. More in detail, thephotosensitive sheet 2 is fixed on the shadow mask 1 at those portionswhich do not contribute to the formation of the phosphor screen by meansof a bonding agent 3b put on the frame as shown in FIG. 2 or on the sideface 3a of the shadow mask 1 engaged with the frame 3 or on both of theframe and the side face. This process requires to be followed for thereasons that in the event of the bonding agent being put substantiallyover the whole interface between the transparent layer 2b and the shadowmask 1, the transparent sheet 2 cannot be removed easily from the shadowmask 1 which may cause the shadow mask to be deformed, and further lightis less easily passed through the shadow mask assembly at thelater-described process of light-exposure.

If desired, wrinkles, if any, of the photosensitive sheet 2 may beremoved by application of heat thereto even after the disposition of thephotosensitive sheet 2. The photosensitive layer 2a may consist ofpolyvinyl chloride, natural rubber, synthetic rubber or the like whichloses viscosity by photopolymerization in the presence of light or mayconsist of polyvinyl-carbazole which is accompanied by a change in itscharged condition in the presence of light.

As the next step, the photosensitive sheet 2 is exposed to light with ahigh-pressure mercury lamp (not shown) through an opening 1c of theshadow mask 1 from the electron gun side lb of the shadow mask 1 asindicated by the arrow in FIG. 1. In the process, assuming that thephotosensitive layer consists of a material subjecttophotopolymerization, the temperature may be within the range from theroom temperature to 90C preferably40 C in order to increase thephotosensitivity of the photosensitive layer. 60C is the mostappropriate for the exposure. Light transmitted through the opening 1cof the shadow mask 1 reaches the photosensitive layer 2a through thetransparent layer 2b, while being attenuated due to absorption andscattering in the transparent layer 2b. As a result, the light-exposedportion 4 of the photosensitive layer 2a in registration with theopening 1c of the shadow mask 1 is smaller in diameter than the openingof the shadow mask 1, as illustrated in FIG. 3.

Particles of an opaque material 5 such as carbon or graphite with thesize of 20 60 millimicrons are sprayed uniformly over the photosensitivelayer 2a. Those of the particles on the light-exposed portions 4 areremoved by the well-known method such as air blast or immersion in asolvent. Although the need of this process may seem to be eliminated bythe laterdescribed process of washing, the removal of the particles asmentioned above is desirable to assure successful results of the washingprocess. Thus, the lightexposed portions 4 are rendered light-transsibleand a layer of the opaque material 5 is formed on the photosensitivelayer 2a except on the light-exposed portions 4, thereby forming in thephotosensitive sheet 21 a light-transmissible portion of a smallerdiameter than the opening of the shadow mask 1. Subsequently, thephotosensitive sheet 21 should be washed with a detergent solutioncontaining an anionic surfactant such as an alkali salt of higher fattyacid, alkyl sulfate, alkylaryl sulfonate, or sulfosuccinic acid ester sothat the light-exposed portions are melted off thereby to clearly definethe boundaries for the light-transmissible portion or to produce awell-shaped light-transmissible hole.

In an example, a photosensitive layer 2a consisting of viscous naturalrubber and having a thickness of 1 micron is exposed to light from amercury lamp off400 W located 30 cm away through shadow mask openingshavinga diameter of'0.32 mm and through a transparent layer 2b having athickness of 8 microns to form light-exposed portions in thephotosensitive layer 2a, and then carbon particles of millimicrons aresprayed on the photosensitive layer 2a. The photosensitive layer 2a isprocessed with an air blast in order to remove particles on thelight-exposed portions no longer having viscosity and thenis washed bythe immersion thereof in a 0.5 percent aqueous solution of sodiumalkylbenzenesulfonate for 30minutes. During the washing processattention should be paid so as not tosubject the'inner side of theshadow mask assembly to the detergent solution, because otherwise theclose contact between the shadow mask and the transparent sheet may belost. In this way, the light-transmissible holes 4 having a diameter of0.23 mm are obtained. In addition to the above-mentioned immersion,spraying may be employed to wash away the light-exposed portions of thephotosensitive layer with a detergent solution, also paying attention asabove mentioned.

The photosensitive layer 2a may consist of such a material as polyvinylcarbazole so that electric charges in the light-exposed portions 4 areremoved by exposure to light for the repulsion of the opaque material.An exposure process to form a phosphor screen is followed through theshadow mask 11 having the photosensitive sheet 21 i. e., through theshadow mask assembly. In the above-mentioned method, a panel for thecathoderay tube with phosphor dots smaller in diameter than the openingof the shadow mask is obtained much more easily than the conventionalmethod employing postetching. Upon completion of the exposure process,the photosensitive sheet 21 fixed at the side face of the frame 3 iseasily removed to recover a desired shadow mask 1.

In addition to a color cathode-ray tubeof shadow mask type referred toabove, the present invention is easily applicable to a color cathode-raytube of chromatron type. v

As is apparent from the foregoing detailed description, in the presentinvention a transparent sheet is put transmissible portion smaller thanthat of the shadow mask opening and at least the photosensitive layer iswashed thereby to form a light-transmissible hole in the photosensitivelayer. Unlike the conventional methods, the present invention has theadvantages that no special measures are required to prevent partialcorrosion of the shadow mask and to maintain the diameter of the openingthereof. In particular. the process of washing the photosensitive layerwith a detergent solution contributes to the clarification of theboundaries for improved dimensional accuracy for the light-transmissibleholes in the photosensitive layer. Furthermore, the method of theinvention has the advantage of the case with which the phosphor screenis produced economically with very few substandard products.

What is claimed is:

1. In a method for making a phosphor screen of cathode-ray.tubecomprising the steps of providing a transparent layer on that surface ofa shadow mask which faces the phosphor screen within said cathode-raytube,

said shadow mask being carried by a supporting frame,-

said transparent layer being capable of attenuating light passingtherethrough, providing a photosensitive layer on said transparent layersaid photosensitive layer upon exposure to light being removable bywashing with a detergentlsolution, exposing said photosensitive layer tolight through said shadow mask and transparent over a shadow'mask tomake the size of the light- 1 layer to form light-exposed portionssmaller in diameter than the shadow mask openings in said photosensitivelayer, developing said photosensitive layer with a light absorbingmaterial that adheres to the unexposed portions to form, in accordancewith the shadow mask openings, a pattern of efiectivelight-transmissible holes in said photosensitive layer thereby obtaininga shadow mask assembly, and forming a pattern of phosphors using saidshadow mask assembly, the improvement comprising the fact that prior tothe formation of the phosphor pattern, said shadow mask assembly iswashed with a detergent solution to remove said lightexposed portions ofsaid photosensitive layer.

2. The method according to claim 1, in which said detergent solutionincludes an anionic surfactant.

3. The method according to claim 1, in which said an ionic surfactant isselected from the group consisting of alkalisalt of higher fatty acid,alkyl sulfate, alkylaryl sulfonate, alkyl sulfonate and sulfosuccinicacid ester.

4. The method according to claim 1, in which said transparent andphotosensitive layers are fixed at those portions which do notcontribute to the formation of said phosphor pattern.

5. The method according to claim 1, in which said photosensitive layerincludes a material capable of photopolymerization and said exposingstep is carried out at a temperature within a range from roomtemperature to C.

1. IN A METHOD FOR MAKING A PHOSPHOR SCREEN OF CATHODE-RAY TUBECOMPRISING THE STEPS OF PROVIDING A TRANSPARENT LAYER ON THAT SURFACE OFA SHADOW MASK WHICH FACES THE PHOSPHOR SCREEN WITHIN SAID CATHODE-RAYTUBE, SAID SHADOW MASK BEING CARRIED BY A SUPPORTING FRAME, SAIDTRANSPARENT LAYER BEING CAPABLE OF ATTENUATING LIGHT PASSINGTHERETHROUGH, PROVIDING A PHOTOSENSITIVE LAYER ON SAID TRANSPARENT LAYERSAID PHOTOSENSITIVE LAYER UPON EXPOSURE TO LIGHT PASSING THERETHROUGH,PROVIDING WITH A DETERGENT SOLUTION, EXPOSING SAID PHOTOSENSITIVE LAYERTO LIGHT THROUGH SAID SHADOW MASK AND TRANSPARENT LAYER TO FORMLIGHT-EXPOSED PORTIONS SMALLER IN DIAMETER THAN THE SHADOW MASK OPENINGSIN SAID PHOTOSENSITIVE LAYER, DEVELOPING SAID PHOTOSENSITIVE LAYER WITHA LIGHT ABSORBING MATERIAL THAT ADHERES TO THE UNEXPOSED PORTIONS TOFORM, IN ACCORDANCE WITH THE SHADOW MASK OPENINGS, A PATTERN OFEFFECTIVE LIGHTTRANSMISSIBLE HOLES IN SAID PHOTOSENSITIVE LAYER THEREBYOBTAINING A SHADOW MASK ASSEMBLY, AND FORMING A PATTERN OF PHOSPHORSUSING SAID SHADOW MASK ASSEMBLY, THE IMPROVEMENT COMPRISING THE FACTTHAT PRIOR TO THE FORMATION OF THE PHOSPHOR PATTERN, SAID SHADOW MASKASSEMBLY IS WASHED WITH A DETERGENT SOLUTION TO REMOVE SAIDLIGHT-EXPOSED PORTIONS OF SAID PHOTOSENSITIVE LAYER.
 2. The methodaccording to claim 1, in which said detergent solution includes ananionic surfactant.
 3. The method according to claim 1, in which saidanionic surfactant is selected from the group consisting of alkali saltof higher fatty acid, alkyl sulfate, alkylaryl sulfonate, alkylsulfonate and sulfosuccinic acid ester.
 4. The method according to claim1, in which said transparent and photosensitive layers are fixed atthose portions which do not contribute to the formation of said phosphorpattern.
 5. The method according to claim 1, in which saidphotosensitive layer includes a material capable of photopolymerizationand said exposing step is carried out at a temperature within a rangefrom room temperature to 90*C.